Diff countries adopt to diff standard of gauge when it comes to rly tracks. While thr freight started its journey from China & travelled through 6 diff countries each of them will have diff track gauge. Some may prefer Broad gauge, few other may prfer std gauge etc.. So intercontinental transshipment of goods always happens in containers because the containers can be mechanically fork lifted & transferred to flat wagons as per the standards & specifications of gauge measurements of that country. Obviously the process is time consuming& often these things happen near the border checkpost which invites custom clearance & other legal matters which adds delay to the process. Hats off China with coordination to all these nations has taken only 2 weeks to cover a mammoth 13000 km